Conservation of energy problem help

In summary, the conversation discusses a problem involving a rod of mass 1g and length L that is held in place against a vertical wall by a cable. A sign of mass 10kg is also hanging off the end of the rod. The conversation focuses on finding the tension in the cable and determining if it can hold the weight. It also mentions finding the normal force from the wall on the rod and the possibility of friction between the wall and the rod. The conversation concludes with a discussion on how to find the tension in the cable using torque.
  • #1
chexmix08
6
0

Homework Statement


1. Consider a rod of mass 1g and length L, held in place against a vertical wall by
a cable at the opposite end as shown in the diagram. A sign of mass 10kg is also
hanging o the end of the rod furthest from the wall. The angles marked are 30 degrees
and 45 degrees .
(a) (10 points) Find the tension in the cable. (Hint: Is the mass of the rod negligible
here? Then clearly mark your pivot point and start summing your
torques.) If the cable has a breaking point of 1000N, will it hold?
(b) (10 points) Find the normal force from the wall on the rod and explain
whether or not there must also be friction between the wall and the rod in
this particular problem. If so, give the magnitude and direction of the friction
force required. (Hint: you will need to draw a diagram and sum the forces.)



Homework Equations





The Attempt at a Solution


- the rod has a mass of 1kg
er 1g
hm i guess its negilible
so sign is 1kg, its 1L away from the pivot point
torque is force times distance
is torque caused by the rod is 1kg*1L*10m/s^2

I'm not really sure how to figure this out, but that is how far I got
 
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  • #2
diagram?
 
  • #3
here's the attached diagram
 

Attachments

  • ll.png
    ll.png
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  • #4
Is the rod of MASS = 1 gram or has WEIGHT = 1 x g = 10N where acc due to gravity is taken as 10m/s^2?

To find the tension it is best to find moments about the pivot so that forces at the pivot will not enter the equation.
 
  • #5
i still don't understand...:confused:
 
  • #6
Do you know how to find moment of a force about a point?
 
  • #7
I think you know.
Moment =torque
 
  • #8
no i don't what does that mean
 
  • #9
how do find the tension the cable
 
  • #10
torque of a force about a point = force x perpendicular distance of line of action of force from the the given point.

hence

torque of 100N from point of attachment of cable with wall = 100 x L sin45.

What is the torque of the weight of the rod, 10N with the same point of attachment?
 
  • #11
so if i do 1000Nsin45 will that be correct
 
  • #12
Some help so that you can try to correct your last post:

As I told you before

torque of a force about a point = force x perpendicular distance of line of action of force from the the given point

therefore torque of weight of rod about point point of attachment of cable with wall =
weight x perp dist of line of action of W with point of ...
= 100 x ...
 

1. What is the conservation of energy principle?

The conservation of energy principle states that energy cannot be created or destroyed, it can only be transformed from one form to another. This means that the total amount of energy in a closed system remains constant over time.

2. How does the conservation of energy apply to real-world situations?

The conservation of energy applies to all physical processes in the universe, from the movement of objects to the chemical reactions that occur in our bodies. It is a fundamental law of nature and is used in various fields such as physics, chemistry, and engineering.

3. What types of energy are conserved?

All forms of energy, including kinetic energy, potential energy, thermal energy, and electromagnetic energy, are conserved. This means that the total amount of these energies in a system will remain the same, even if they are converted into different forms.

4. How can the conservation of energy be applied to solve problems?

Conservation of energy can be used to solve problems by using the principle that the total energy before and after a process must be the same. This can be applied in various scenarios, such as calculating the speed of an object after falling a certain distance, or determining the final temperature of a system after a chemical reaction.

5. Are there any exceptions to the conservation of energy principle?

The conservation of energy is a well-established principle, but there are some scenarios where it may not hold true. For example, during nuclear reactions, a small amount of mass can be converted into energy according to Einstein's famous equation, E=mc². However, in everyday situations, the conservation of energy principle is a reliable guideline for understanding physical processes.

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